1. Field of the Invention
The present invention relates to a method and a mold for manufacturing a golf ball.
2. Description of the Related Art
A conventional method for manufacturing a core of a multiple piece golf ball, such as a two-layer core, or a three-layer core, is described below.
In FIG. 11A, a mold for preliminary forming rubber shells having a lower mold 31 and an upper mold 35 is shown. The lower mold 31 has a pair of mold halves 30 connected by a hinge. Each of the mold halves 30 is provided with hemispherical concave portions 32. The upper mold 35 is provided with hemispherical convex portions 34 corresponding to the concave portions 32. As shown in FIGS. 11B, 11C and 11D, an unvulcanized rubber material 33 is placed into each of the concave portions 32, and the upper mold 35 is lowered to press the rubber materials 33 against the lower mold 31. Thus hemispherical unvulcanized rubber shells 36 are formed.
After that, as shown FIG. 11E, a vulcanized inner core 37 is placed into each of the unvulcanized rubber shells 36 formed on each of the concave portions 32 of either one of the mold halves 30. Then as shown in FIG. 11F and FIG. 12A, the other mold half 30 is folded so as to be placed on the mold half 30 containing the inner cores 37, after which the mold is closed, and pressed. Thus the inner cores 37 are covered with the unvulcanized rubber shells 36 formed on the other mold half 30, as shown in FIG. 12B. That is to say, each of the inner cores 37 is covered with each pair of the unvulcanized rubber shells 36 to form spherical intermediate products 38. Then, as shown in FIG. 12C, ejectors 39 provided on one side of the mold halves 30 are moved to eject the products 38. The products 38 are then set in a mold for vulcanization molding 40 as shown in FIG. 12D, and the unvulcanized shells 36 of the products 38 are vulcanized to form cores, not shown.
In the conventional method described above, there is a problem in the process of covering the inner cores 37 with the shells 36 such that the inner cores 37 are moved by the process pressure and become greatly eccentric.
There is also a quality problem of the cores wherein a connected face, or the joint of each pair of the shells 36 which cover the inner core 37 sometimes becomes separated. To prevent the separation of the connected faces, the temperature of the mold in the process of covering, the temperature of the rubber materials, the pressure applied to the mold in the pressing process, and the pressing time of the pressing process are optimized. However, the separation of the connected faces can not be prevented completely. Moreover, it is not possible to produce a large number of cores at one time using the conventional method.
It is therefore an object of the present invention to provide a method for manufacturing a golf ball which greatly reduces the eccentricity of an inner core of a golf ball whereby a golf ball of high quality can be effectively manufactured. It is another object of the present invention to provide a mold and a method for manufacturing a golf ball wherein a large number of cores are manufactured at one time.